diff --git a/.github/workflows/ur-build-hw.yml b/.github/workflows/ur-build-hw.yml
index f8d029ae537a2..cf6f6b6972d28 100644
--- a/.github/workflows/ur-build-hw.yml
+++ b/.github/workflows/ur-build-hw.yml
@@ -43,6 +43,10 @@ env:
   UR_LOG_NATIVE_CPU: "level:error;flush:error"
   UR_LOG_OPENCL: "level:error;flush:error"
 
+# Free disk on the runner host before Docker must be enforced with a self-hosted
+# job-started hook (same machine as the job). A separate workflow job with the
+# same runs-on labels can land on a different host. See:
+# devops/scripts/gha_runner_job_started_hook.sh
 jobs:
   adapter_build_hw:
     name: Build & CTS
diff --git a/.github/workflows/ur-build-offload.yml b/.github/workflows/ur-build-offload.yml
index a525cb8d799b2..dd3de98fb8c6c 100644
--- a/.github/workflows/ur-build-offload.yml
+++ b/.github/workflows/ur-build-offload.yml
@@ -2,6 +2,8 @@ name: UR - Build offload adapter
 
 permissions: read-all
 
+# Pre-container disk check: use ACTIONS_RUNNER_HOOK_JOB_STARTED on self-hosted
+# runners — see devops/scripts/gha_runner_job_started_hook.sh
 on: [ workflow_call, workflow_dispatch ]
 
 jobs:
diff --git a/devops/scripts/gha_runner_job_started_hook.sh b/devops/scripts/gha_runner_job_started_hook.sh
new file mode 100644
index 0000000000000..f6682ef7c91ec
--- /dev/null
+++ b/devops/scripts/gha_runner_job_started_hook.sh
@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Self-hosted GitHub Actions runner — job-started hook (runs on the HOST).
+#
+# Configure on each runner machine, e.g. in the service environment:
+#   ACTIONS_RUNNER_HOOK_JOB_STARTED=/path/to/llvm/devops/scripts/gha_runner_job_started_hook.sh
+#
+# GitHub runs this after a job is assigned to this runner but BEFORE the job
+# container is created, so the check applies to the same host that will pull
+# and run Docker (unlike a separate workflow job with the same runs-on labels,
+# which may run on a different machine in the pool).
+#
+# Optional: UR_CI_MIN_FREE_DISK_MB (default 20480) — minimum free space on / in MiB.
+#
+# https://docs.github.com/en/actions/hosting-your-own-runners/managing-self-hosted-runners/running-scripts-before-or-after-a-job
+
+set -euo pipefail
+
+MIN_MB="${UR_CI_MIN_FREE_DISK_MB:-20480}"
+
+if ! command -v df >/dev/null 2>&1; then
+  echo "WARNING: df not available; skipping UR CI disk preflight"
+  exit 0
+fi
+
+avail_kb="$(df -Pk / | awk 'NR==2 {print $4}')"
+avail_mb=$((avail_kb / 1024))
+
+echo "gha_runner_job_started_hook: free on / = ${avail_mb} MiB (minimum ${MIN_MB} MiB)"
+
+if [ "$avail_mb" -lt "$MIN_MB" ]; then
+  echo "ERROR: insufficient disk space on runner host (${avail_mb} MiB free, need at least ${MIN_MB} MiB)"
+  exit 1
+fi
+
+exit 0